• Rural NZ
• Adverse Events
• People issues
• Profitability
• Research
• Rural Proofing
• SLM Hill Country Erosion Programme
• Community Irrigation Fund
• Stats & forecasts
• Sustainability
  • Best practices
  • Biodiversity
  • Climate
  • Irrigation
  • Land
  • Native forests
  • Organics
  • Resources
  • Water
• Legislation
• Media Centre
• Publications
• What's New

Report One: Cadmium in New Zealand Agriculture

Chapter 2: Current management approaches for cadmium in New Zealand

General approaches to the management of soil contaminants

Mass balance versus risk-based approaches

There are two approaches that are commonly used to ensure the safe management of contaminants; the "mass balance" approach or the "risk-based" approach. These two approaches have quite different philosophical underpinnings, and can result in different management regimes.

Mass balance approach

Some northern European countries aim to minimise or avoid any accumulation of heavy metals stemming from human activities. This method generally uses mass-balance modelling, synthesising information on heavy metal inputs and outputs, to find a level of input which can be applied over time without causing net accumulation (Molloy et al, 2005). In effect, this approach aims to maintain background or current heavy metal concentrations indefinitely, unrelated to any perceptions of the risk attributable to the base level of the contaminant.

Countries which have used this approach, such as Sweden, Norway and Denmark, also tend to favour stricter standards for the permissible levels of various metals in sewage sludge (Renner, 2000).

Risk based

Other countries have set standards for the inputs of metals into soil by taking a risk-based approach. This method, rather than trying to avoid any build-up of metals, aims to determine the levels of metal in soils which represents an acceptable risk (Renner, 2000). Often this approach will determine the level at which adverse impacts are observed (on the environment or to human health, or both), and then set a soil concentration limit or trigger level below this level, allowing for a safety margin (ibid).

Examples of countries that use risk-based methodologies to determine safe levels of contaminants in soils include the United States, Australia under National Environmental Protection (Assessment of Site contamination ) Measure (1999) for human health protection, the United Kingdom and the Netherlands (Renner, 2000).

The mass-balance and the risk-based methods have different advantages and disadvantages. The risk based approach can involve a significant level of uncertainty (knowledge of ecological systems and interactions has many significant gaps) and subjective judgment and assumptions (deciding whether risk to people, animals, plants, or entire ecosystem function should be considered, as well as deciding what constitutes "acceptable" risk) and can produce varied results. The "no-net-accumulation" approach, on the other hand, can be unnecessarily restrictive, as it can peg input levels (from fertiliser, biosolids or manure) at levels far below what would begin to pose a risk to people or ecosystems. If this is the case, land managers are effectively burdened with costly restrictions beyond what is appropriate to ensure safe agricultural practices.

The risk-based approach fits with New Zealand’s environmental management framework, as set out by the "effects-based" Resource Management Act 1991. The Ministry for the Environment’s contaminated land management guidelines which provide guidance to regional councils on selection and applying environmental guideline values (that is, soil limits) also advise taking a risk-based approach to setting guideline values. Guideline number two (Hierarchy and Application in New Zealand of Environmental Guideline Values (MfE 2003)) provides guidance to all organisations on selecting contaminated site assessment guideline values. Food safety administration in New Zealand is moving towards a risk-based approach to food safety management, in line with international trends (FAO, 2004).

It is appropriate that the management of cadmium in soil be based on "risk assessment", rather than taking the "no-net-accumulation" approach. If inputs exceed outputs then a risk based approach will result in soils cadmium eventually reaching a specified guideline value and a mass balance approach will need to be adopted at that stage.

New Zealand’s management of cadmium in, or relating to, agricultural systems is obscure, relying on a range of central government legislation, guidelines and local government controls. Central and local government have developed these measures to protect the environment, including the health and well-being of people and communities.

Current management of contaminants in New Zealand

The Resource Management Act

The Resource Management Act 1991 (RMA) is the core piece of legislation controlling how our use of the environment is managed. The RMA contains defines "contaminated land", requires planning controls to manage the discharge of hazardous substances and effects of these substances in or on land. The RMA also defines functions for local government in relation to contaminated land. Under the RMA, the bulk of decision-making authority rests with local government.

Definition of contaminated land

Contaminated land is defined in section 2 of the RMA as land that has hazardous substances³ in or on it and:

1. is more contaminated than an applicable National Environmental Standard,⁴ or
2. has, or is reasonably likely to have, significant adverse effects on the environment.

While cadmium on its own may be classed as a hazardous substance, fertiliser containing cadmium is not.

Discharges

While fertiliser is not a hazardous substance, it is generally considered a “contaminant” as defined under the RMA. The discharge of “contaminants” requires resource consent under section 15 of the RMA unless permitted by a rule in a plan. Regional plans generally have a rule permitting fertiliser being applied to land.

Roles and functions under the RMA

The Ministry for the Environment

As the Government’s key advisor on the New Zealand environment, a function of the Ministry for the Environment is to provide advice on contaminated land issues. The function of the Minister for the Environment includes developing National Environmental Standards under the RMA. The Ministry is responsible for administering the RMA, and works in partnership with key sectors, organisations and communities to improve our environment.

Local government

Local government consists of regional councils and territorial authorities each with a specific contaminated land function under the RMA (see Box 1). Each council controls the activities in its area through policies and rules in district and/or regional plans. All land users must ensure their activities comply with the requirements of these plans and the RMA. Resource consents may be required for changes in land use, activities that have the potential to contaminate land, and activities on contaminated land. However, the requirements and the thresholds will vary between districts and between regions.

Because each council prepares its own plans, there is a lot of variability between plans in how they address contaminated land. A recent review of contaminated land provisions in district, regional and unitary plans highlighted the extent of this variability (Ministry for the Environment, 2006c). The review of district and city plans showed that:

• 33 percent of district and city plans featured no specific provisions relating to contaminated land;
• approximately 40 percent of plans have specific objectives, policies and rules relating to land use or remediation of contaminated land; and
• of the plans that have specific provisions, there is significant variability in how contaminated land is addressed.

Regional plans and policy statements are more consistent. Most regional plans address contaminated land, with 88 percent having specific provisions. However, there is still significant variation in terms of how each plan addresses contaminated land. Almost all regional policy statements prepared by regional councils under the RMA (15/16) contain objectives that as a minimum “highlight the need to manage the risks associated with contaminated sites on the environment (variously including protection of water ecosystems, land ecosystems, air resources, control of waste, community well being, human health and safety, etc)”. Most regional policy statements (13/16) also, as a minimum, contain methods requiring the investigation of contaminated sites by the Regional Council (MfE, 2006)⁵.

National Environmental Standards

The RMA enables the Minister for the Environment to prepare "National Environmental Standards" (hereon called standards). These standards have the force of regulations and are binding on local authorities. They can be established for a number of matters, including contaminants, or soil quality in relation to the discharge of contaminants.

There are currently no standards set out in regulation for contaminants in soil. However, the Ministry for the Environment has recently confirmed a work programme that includes:

“Develop a standard and supporting guideline that provides:

1. a nationally consistent New Zealand based methodology for deriving soil contaminant levels for human health
2. numerical criteria for priority contaminants that define appropriate management actions that is the numerical criteria may:
   1. serve as conservative cleanup targets
   2. inform onsite management actions to reduce the potential for adverse effects
   3. trigger further investigation to determine site specific criteria.”

To develop the standard a technical working group will be convened. This group will build on the work of a previous working group and is anticipated to have a similar membership. Membership will comprise of the relevant central government agencies (Ministry of Health, Ministry of Agriculture and Forestry, Environmental Risk Management Authority and New Zealand Food Safety Authority), and invite technical advice from local government and industry.

Guidelines and standards for contaminants in soil

Soil standards and guidelines provide a means for contaminant levels in soils to be monitored, evaluated and managed. Standards are defined in this report as legally enforceable numbers while guidelines are voluntary (see Box 2 for more discussion on the difference between standards and guidelines)

Guidelines

There is a range of New Zealand guidelines for contaminants in soil, as well as guideline values used internationally to monitor and manage contaminant levels in soils.

The Ministry for the Environment, in consultation with industry and local government, has developed a series of contaminated land management guidelines. These guidelines support the relevant local government functions under the RMA. The guidelines cover the following topics:

• Reporting on contaminated sites (Ministry for the Environment, 2003a)
• Hierarchy and application in New Zealand of environmental guideline values (Ministry for the Environment, 2003b)
• Risk screening system (Ministry for the Environment, 2004a)
• Classification and information management protocols (Ministry for the Environment, 2006b)
• Site investigation and management of soils (Ministry for the Environment, 2004b).

The Ministry also developed or supported a number of guidelines containing soil guideline values for specific contaminants of concern.

There are two New Zealand guidelines containing soil guidelines values for cadmium:

• The “New Zealand Water and Wastes Association (NZWWA) guidelines for the safe application of biosolids to land in New Zealand” (NZWWA, 2003). These "risk based" guidelines specify a 1 mg/kg soil limit for cadmium, above which the application of biosolids to land should cease. This soil limit is not specified for particular land uses, rather the soil limit is recommended for all soils where biosolids are used in New Zealand. The biosolids guidelines for cadmium were developed to protect against the uptake of cadmium into crops that are consumed by people, protect soil microbial health and to protect international trade against food standard exceedences.
• “The Australian and New Zealand Guidelines for the Assessment and Management of Contaminated Sites” (ANZECC 1992). The guidelines include "threshold based" cadmium ingestion levels for human health of 20 mg/kg and for environmental soil quality of 3 mg/kg. These guidelines have been largely superseded by the Ministry for the Environments contaminated land management guideline series.

The contaminated land management guideline series and the biosolids guidelines are widely used in New Zealand, at least by regional councils and unitary authorities ⁶, and are reported by users as being technically robust. While guidelines containing soil contaminant values like the biosolids guidelines have been written for a specific activity (biosolids application) the values are generally transferable to other activities that share similar hazardous substances. For example, the NZWWA biosolids guideline has been used by some regional councils to measure and assess cadmium present in soils as a result of phosphate fertiliser application, rather than the application of biosolids.

Although the level of use by territorial authorities has not been surveyed, it is likely to be much more variable.

Because the way the land is used influences the level of risk posed by a contaminant, guidelines generally specify guideline values for a range of land use scenarios (for example, residential, agricultural, industrial/commercial). Higher levels of contaminants are usually accepted in soil which is used for high-density residential or industrial purposes, because the ground itself is likely to be covered by buildings or concrete, and thus people will have little or no contact with either the soil or food grown in the soil.

Agricultural standards or guidelines could be expected to be more stringent, as the soil is used for the purposes of growing food, which creates a potential "pathway" by which people become exposed to cadmium (or other hazardous substances).

Guidance on the use of environmental guideline values

Typically, New Zealand practitioners rely on a mixture of national and international guidelines from which to select numerical values. However, the various New Zealand and international guidelines used contain different terminology and methodologies.

To reduce the confusion created by these differences, the Ministry for the Environment produced a guideline, in partnership with local government, called “Contaminated Land Management Guidelines No. 2: Hierarchy and Application in New Zealand of Environmental Guideline Values” (Ministry for the Environment, 2003b). CLMG No. 2 provides a best-practice hierarchy for selecting guidelines from the range of New Zealand and international guidelines available. CLMG No. 2 states a preference for New Zealand guideline values over international guidelines, and a preference for risk-based guideline values over threshold values. Based on these preferences, CLMG No. 2 sets out the following hierarchy for selecting guideline values:

1. New Zealand-derived, risk-based guideline values;
2. Rest-of-the-world-derived risk-based guideline values, with a preference given to those that employ risk assessment methodologies and exposure parameters consistent with what is already used in New Zealand;
3. New Zealand-derived threshold values;
4. Rest-of-the-world-derived threshold values.

Issues associated with the use of guidelines for assessing cadmium in soil

Councils may choose different guideline values: The guideline value chosen by a council has the potential to have significant consequences for landowners and their land-use choices.

CLMG#2 outlines the best practice approach to selecting guideline for contaminants in soil. It is expected that this hierarchy should be followed. For example, Section 5.3 of Contaminated Land Management Guideline #5: Site Investigation and Analysis of Soils, entitled “Use and misuse of guidelines”, notes:

“Only guideline documents that are appropriate to the site conditions should be used, and you should have a thorough understanding of the basis of the derivation of the guideline numbers. Contaminated Land Management Guidelines No. 2: Hierarchy and Application in New Zealand of Environmental Guideline Values (Ministry for the Environment, 2003b) should be followed.”

However, some local authorities may be unaware of this expectation, or may choose not to follow a recognised best practice approach. This can lead to adoption of inappropriate guideline values in some cases.

Some variations may occur between areas or regions when applying CLMG#2. For example, CLMG#2 leads to selection of the United Kingdom’s figures of 1, 2 and 8 mg/kg for cadmium in residential soil of pH 6, 7 and 8. This can lead to a situation where different guidelines may apply to different properties due to either natural differences in soil pH, or use of lime on a particular site as a specific remediation measure.

Councils may apply guideline values differently:Councils may choose to apply trigger values (values which, if exceeded, "trigger" a further investigation to assess the level of contamination) as threshold values (a number which, simply applied, everything coming under is "not contaminated" and everything exceeding the threshold is ‘contaminated’).

This is mostly determined by the context of a particular investigation. In specific contaminated sites investigations, risk-based guidelines (ideally selected according to CLMG#2) are usually used to delineate the areas of contamination and act as de facto clean-up targets. Site-specific guidelines may also be developed, depending on the size and complexity of the site. By contrast, in regional council State of the Environment (SoE) surveying, guidelines are mostly used as trigger levels to denote the presence of an issue that may warrant closer investigation.

One significant difference between state of the environment surveying and contaminated site investigations is in the amount of attention paid to specific properties. State of the Environment surveying of soil involves sampling of one part of a property, with each location becoming merely one survey point in a larger network. Contaminated sites investigations are quite different, because these represent the detailed site-specific investigation of a single property. Exceeding a soil guideline in a single composite soil sample collected from a given property is not equivalent to identifying that property as a contaminated site. The detailed requirements of contaminated sites investigations are provided in the Ministry for the Environment’s Contaminated Land Management Guidelines series (most specifically CLMG#1, CLMG#2 and CLMG#5).

Guidelines do not specify a sampling depth or method: Cadmium tends to accumulate in the topsoil, because it is applied to the surface of the soil (via fertiliser) and binds reasonably strongly to the soil (Gray et al, 2003).

The Ministry for the Environment’s CLMG#5 provides guidance on soil sampling, including the range of sampling approaches that can be applied, the need to collected representative soil samples, and sampling depths applicable to surface soils (Section 3.6.2 of CLMG#5). The context of this guidance is contaminated site investigation.

Sampling depth is an important consideration when interpreting the applicability of guidelines. Guidelines are not provided with sampling depths attached, because these may vary depending on context. At contaminated sites it is relatively common to encounter pockets of contamination at a range of different depths, depending on the site history. Among experienced practitioners it is well understood that for any risk-based guideline, the sampling depth should aim to represent the key exposure pathways that were considered in the development of the guideline, and given the specific characteristics of the site. However, a lack of familiarity with this area may lead to some inconsistency between approaches taken by different councils

Voluntary industry limits on cadmium content of fertiliser

For some time (since 1995), the New Zealand fertiliser industry has had in place voluntary standards for the levels of cadmium in phosphate fertilisers. These voluntary standards were negotiated by the New Zealand Fertiliser Manufacturers’ Research Association (NZFMRA) and fertiliser companies. The new lower limits agreed to by industry were:

• July 1995 to Dec 1996 - 340 mg cadmium/kg P;
• Jan 1997 onwards - 280 mg cadmium/kg P.

As part of this voluntary reduction policy, the cadmium content of phosphate fertilisers was incorporated into the Fertiliser Quality Councils’ Fertmark quality assurance programme administered by Federated Farmers and subject to independent audit. The independent audit for the period January 2001 - June 2005 showed that the weighted average of cadmium content of phosphate fertilisers was between 149 mg cadmium/kg P and 193 mg cadmium/kg P. During this period no samples exceed the industry voluntary maximum of 280 mg cadmium/kg P.

Fertiliser manufacturers took the decision that no sample should exceed the 280 mg cadmium/kg P level - regardless of sampling or analytical error. This means that manufacturers need to produce single superphosphate with a cadmium content well below the 280 mg cadmium/kg P level.

In addition fertiliser recommendations for cropping situations where high phosphate inputs (for example, potato, onion) have advocated for the use of high analysis NPK fertilisers. These fertilisers generally have a lower cadmium content than straight single superphosphate.

However, it should also be recognised that neither the voluntary industry limit, nor the weighted average cadmium contents achieved are yet sufficiently low to prevent cadmium from accumulating in New Zealand’s agricultural soils as a result of phosphate fertiliser use. The overall average for cadmium in phosphate fertilisers over the last five year period (2001- 2005) has been 175 mg cadmium/kg P.

Chapter summary

In New Zealand, there are systems currently in place to manage the different risks arising from cadmium in soils, food and phosphate fertiliser.

There are currently no official national-level standards for the permissible amount of cadmium in agricultural or residential soils or for the discharge of cadmium onto soil in New Zealand. There are a variety of different guidelines (some developed in New Zealand and others overseas) which councils may use to guide them in this assessment. These guidelines are not legally binding, unless councils give them legal effect by incorporating them into a regional or district plan, (although in court, a robust and credible guideline would have some weight as a widely held definition of "best practice") or as a condition on resource consents.

The Ministry for the Environment has published a "guideline to the guidelines" called the "Contaminated Land Management Guidelines 2" (CLMG#2), which sets out a process for councils to follow select an appropriate guideline value for use in a contaminated site assessment.

The end-result of this regulatory environment is that, following the process set out in the CLMG#2, values currently used by some councils to indicate the requirement for a contaminated site assessment or to determine whether a site should be identified as contaminated on a LIM (Land Information Memoranda) or PIM (Project Information Memoranda) report issued under the Local Government Information and Meetings Act 1987 for cadmium range from 1 mg/kg to 22 mg/kg depending on land use. The guideline value chosen by a local authority has the potential to have significant consequences for landowners and their land-use choices. Guidelines should make reference to soil sampling depth and sampling method, in order to ensure consistency. Analytical methods should also be stipulated, to ensure comparable results.

At the industry level, there has been a voluntary initiative by the fertiliser industry to limit the amount of cadmium present in phosphate fertilisers, which is discussed further in Chapter 3.

References

Gray CW; McLaren RG; Roberts AHC (2003). Cadmium leaching from some New Zealand pasture soils. “European Journal of Soil Science”, Vol 54(1), pp 159-166.

IPCS (1987). “Principles for the Safety Assessment of Food Additives and Contaminants in Food”, International Programme on Chemical Safety, Environmental Health Criteria 70.

Ministry for the Environment (2003a). “Contaminated Land Management Guidelines No. 1: Reporting on Contaminated Sites in New Zealand”. Ministry for the Environment: Wellington.

Ministry for the Environment (2003b). “Contaminated Land Management Guidelines No. 2: Hierarchy and Application in New Zealand of Environmental Guideline Values”. Ministry for the Environment: Wellington.

Ministry for the Environment (2004a). “Contaminated Land Management Guidelines No. 3: Risk Screening Systems”. Ministry for the Environment: Wellington.

Ministry for the Environment (2004b). “Contaminated Land Management Guidelines No. 5: Site Investigation and Analysis of Soils”. Ministry for the Environment: Wellington.

Ministry for the Environment (2006b). “Contaminated Land Management Guidelines No. 4: Classification and Information Management Protocols”. Ministry for the Environment: Wellington.

Ministry for the Environment (2004). Your Guide to the Resource Management Act: an essential reference for people affected by or interested in the RMA. MfE, Wellington.

Molloy R; McLaughlin M; Warne W; Hamon R; Kookana R and Saison C (2005). “Background and scope for establishing a list of prohibited substances and guideline limits for levels of contaminants in fertilisers”. CSIRO Land and Water, Australia.

New Zealand Food Safety Authority (Accessed 27/03/06). Agricultural Compounds and Residues in Food. http://www.nzfsa.govt.nz/consumers/chemicals-nutrients-additives-and-toxins/agricultural-compound-in-food/

New Zealand Water and Wastes Association (2003). “Guidelines for the Safe Application of Biosolids to Land in New Zealand”.

Renner R (2000). Sewage sludge, pros and cons. In “Environmental Science and Technology”. Vol 34, Issue 19.

World Health Organisation (1991). Evaluation of certain veterinary drug residues in food (Thirty-eighth report of the Joint FAO/WHO Expert Committee on Food Additives). WHO Technical Report Series, No. 815, 1991.

³ The RMA section 2 definition of “hazardous substance” includes, but is not limited to, any substance defined in section 2 of the Hazardous Substances and New Organisms Act 1996 as a hazardous substance.

⁴ (a) does not currently apply as there are no national environmental standards for contaminants in soil at the time of publication of this report.

⁵ Contaminated Land – Review of District, Regional and Unitary Plans, unpublished report prepared for the Ministry for the Environment by Rosalind Day – Boulder Planning (Otago) Ltd, June 2006.

⁶ The findings of a June 2006 survey of council officers at 14 of the 16 regional and unitary councils indicated that the guidelines were used by most respondents. The contaminated land management guideline series was used by 85−100 percent of respondents, while the main industry guidelines (timber treatment, oil industry, gasworks and biosolids) were used by most (70−83 percent) respondents (Ministry for the Environment, 2006d). The ANZECC 1992 guidelines were not surveyed.

Contact for Enquiries

MAF Information Services
Pastoral House
25 The Terrace
PO Box 2526
Wellington, NEW ZEALAND

Fax: +64 4 894 0721
Contact this person